I love a third-party verified list, but with green airline itself nudging to the top of the most oxymoronic phrase list I decided to take a look at how Greenopia actually measures the viriditÄs of our domestic airlines.

Greenopia explains their calculations:

In order to rank the various airline chains in the US we collected data from their annual report and compared them to various environmental criteria. These criteria included fleet age, fuel consumption practices, carbon offsets, green building design, recycling programs, and green food items available on flight. Weights were set based off a rough life-cycle of the impacts of air travel.

As the guide also explains, some categories are weighted more than others. For example, food:

Although it constitutes a very small portion of the weighting we still thought it was important to see which airlines had organic, local, natural, or fair trade food items available on flights.

Along with attracting a more food conscious customer, progressive food purchasing presumably indicates a progressive corporate ethic. And it's this ethic that seems to help airlines rank highly throughout the categories. This can be seen in both the carbon offset and recycling categories as well, both of which have a relatively small overall impact on the greenness of an airline, while reflecting a green corporate conscience.

It's The Fuel, Dummy!When it comes right down to it, the fact that airplanes spew forth fossil fuel emissions miles up in the atmosphere is what makes them such heavy polluters. It would follow then that the fuel conservation category would carry the most weight in the rankings.

Although they are unwilling - for competitive reasons - to share specific details about the weighting of the criteria, Greenopia's Research Director Doug Mazeffa confirms this assumption. "The biggest impact a major airline has (by a huge amount) is from the operation of its fleet, weighting is very much geared to focus on this as well."

Current ways that the highly ranked companies reduce their fuel consumption and emissions include using single engines for taxiing, using electric-powered ground vehicles, implementing engine washing programs, and installing winglets to decrease drag.

Mazeffa says that, depending on the exact type, winglets can reduce fuel consumption by 3-5%."This seemingly simple fix really is huge when you look at magnitude of the emissions being discussed."

Greenopia concedes that the use of alternative fuels is fledgling at best in the industry, but includes the pursuit of these fules as a category anyway. "We tend to promote biofuels for airlines because it shows a significant investment in the pursuit of a new technology that can reduce their environmental footprint in other ways than just carbon footprinting," explains Mazeffa. "It's not a very big part of our mathematical weighting and we are extremely optimistic that such fuels can lead to a greater carbon reduction as the technology continues to be further refined."

Isn't One Airline Really Just as Good, or Bad, as the Next?Commercial flight, to my mind, is such an enviro-no-no that it's tough to get my head around the fact that choosing one airline over the next makes a difference. Does it really matter if I fly Virgin or American? (American drags up the rear on the list with a slight verdant pallor.)

According to Mazeffa the answer is actually "yes". Using the concept of emissions per Revenue Passenger Mile (an industry statistic), Virgin tends to be about 10-20% more efficient per mile flown than many of the other airlines. "This may not be true over every single trip possible, but it is when looking at the company-wide metrics."

Unless the solar powered jet engine quickly appears, it's tough to see a green future for the airline industry anytime soon. Even if the entire global fleet of planes is fueled by non food-grade coconut and babassu oil - as one engine was for a much publicized crew-only Virgin flight in 2008 - the industry would have to contract a lot of farmers to grow a lot of babassu on a lot of land that we just might want to keep for food crops. The physics of flight dictates that you need an exceptional amount of fuel to launch hundreds of thousands of pounds into the air and keep it moving for hours at a stretch. That fuel is the bottleneck in allowing commercial flight to be truly green and sustainable.

But, things being what they are, if you gotta fly you gotta fly, and Greenopia's annual ranking is a good reference for making an informed decision.